(A) Field of the Invention
The present invention relates to a method for correlating a structural parameter of a plurality of predetermined gratings and method for determining a structural parameter value of an unknown grating using the same, and more particularly, to a method for correlating a structural parameter of a plurality of predetermined gratings by through focus image acquisition and focus metrics algorithm and method for determining a structural parameter value of an unknown grating using the same.
(B) Description of the Related Art
With the rapid growth and development of the semiconductor industry, the requirement to reduce the critical dimension (CD) and line-width has gradually increased, and the precision of metrology tools must be raised to meet demands. According to Rayleigh criteria, it is quite difficult for conventional image metrology tools to meet the prospective resolution demands due to issues such as optical diffraction, precision of metrology tools and proximity effect. Consequently, it is necessary to find a new metrology to solve the above-mentioned problem.
In addition, the metrology tools for measuring line-width and pitch, such as critical dimension scanning electron microscopes (CD-SEM) and critical dimension atomic force microscopes (CD-AFM) offer very high resolution, but are too expensive for most applications. Users need cost-effective and efficient image metrology tools, which can achieve the same resolution as CD-SEM and CD-AFM.